The incorporation of video projections into a
stage
production can be done in two ways. One is by presenting the video material on an array of video monitors, a so-called Video Wall. The other method is by using a special video
projector
to project the video material onto a
projection
screen or onto any other surface, such as a section of the scenery.
Video material can be edited in advance and recorded on a video cassette or a
laser
video disk, or relayed live from close-circuit television cameras as is the practice in rock and roll concerts and mass events.
The most common video projectors use a system of three tubes, each of which projects one of the three primary colors: red, blue, and green. Electronic control enables regulating the tubes for optimal color separation, and each tube has its own
lens
which focuses the given color
image
on the
projection
screen.
Such video projections are limited by the relatively low
level
of brightness, requiring low levels of
stage
lighting as well as good separation between the
stage
lighting and the
projection
screen. The sharpness of the
projection
is also quite poor compared to that of a film
projector
and will not suffice for large size projections.
A much brighter and sharper video
projection
can be achieved by the much more expensive and complex thin oil film video projectors such as the Gretag Eidophor which has a light output of 2000 lumens and can project pictures as wide as 13 meters. The video
image
is projected on a thin oil surface which passes light. The
projection
system is similar to that of a film projector: the light passes through the thin oil film and is projected onto the screen through a
lens
system. The brightness and sharpness of the thin oil film video
projector
makes the use of large video projections on
stage
practicable.
The conventional three tube video
projector
is now being replaced by liquid crystal (LCD) projectors which are brighter and have a better resolution and color definition. These use a conventional
light source
and an
optical system
similar to those of a
slide
projector. The
slide
in this case is a liquid crystal panel consisting of thousands of miniature liquid cells which act as high speed shutters.
